The invention relates in general to polymers and more particularly to polymers useful as biomaterials. A practical biomaterial must exhibit two important qualities. First, it must possess suitable mechanical properties. For example, if the biomaterial is to be used as a dental implant, it must be hard and rigid. On the other hand, if it is to be used as a diaphragm of an artificial heart which must flex more than 50 million times per year it must have elastomeric bulk properties and endure cyclic deformation and flexing throughout the life of its host. Second, the biomaterial must have a nonthrombogenic surface. The latter requirement is particularly critical since most biomaterial failures are due to the occurrence of thrombogenic responses at the biomaterial's surface. Several approaches have been attempted in order to identify biocompatible surfaces.
In the past, there have been two main approaches to prepare biocompatible surfaces. The first approach has been to attempt to reduce the thrombogenicity of the surface by coating the material's surface with proteins or hydrogels. The second approach has been the surface treatment by three main methods. The first is the ionic binding of heparin onto the surface. The second is the covalent binding of heparin onto a polymer material and the third method is chemical modification of the polymer surface in order to confer heparin like properties.
Ruckenstein and Gourisankar (Ruckenstein, E., and Gourisankar, S., J. Colloid Interface Sci. 101, 436 (1984)) suggested that the surface properties of a biomaterial must be selected such as to have a very low (preferably zero) interfacial free energy between the solid and the environmental liquid, since under such conditions, the thermodynamic driving force for deposition on the surface is very low. Therefore neither proteins or cellular components will deposit on the surface. A very small interfacial free energy (near zero) is, however, undesirable from the point of view of mechanical stability of the interface. Since the cellular elements of blood are compatible with blood, and their interface with the medium (blood plasma) is also mechanically stable, a blood-biomaterial interfacial tension of about the same magnitude as the cell-medium interfacial tension (.gamma..sub.sw .apprxeq.1-3 dyn/cm) might provide a foreign surface with long term compatibility as well as mechanical stability of the interface. Assuming that the surface free energies can be written as the sum of a dispersion and polar component and employing the geometric mean for the interaction energy between the two phases, they conclude that the polar components of bioenvironments (biofluids, blood, marine environment, tear environment etc.) and biomaterial should be near to one another and the dispersion components should satisfy the same condition.